Antidepressants Linked to Improved Verbal Memory

MILAN — Antidepressants escitalopram and duloxetine have been shown to improve verbal memory in moderate to severe depression, a clinical effect linked to changes in serotonin 4 (5-HT4) receptor levels in the brain as shown on PET.
These findings suggested there is a role for specifically targeting the 5-HT4 receptor to improve verbal memory in depression, said investigator Vibeke H. Dam, PhD, from Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark.
“Verbal memory is often impaired in depression, and this has a lot of impact on patients’ ability to work and have a normal life. That’s why we’re so excited about this receptor in particular,” Dam told Medscape Medical News.
“If we can find a way to activate it more directly, we’re thinking this could be a way to treat this memory symptom that a lot of patients have and that currently we don’t really have a treatment for,” she added.
The findings were presented on September 23 at the 37th European College of Neuropsychopharmacology (ECNP) Congress and recently published in the journal Biological Psychiatry.
Largest Trial of Its Kind
The study is the largest single-site PET trial investigating serotonergic neurotransmission in major depressive disorder over the course of antidepressant treatment to date.
It included 90 patients with moderate to severe depression who underwent baseline cognitive tests and brain scans to measure 5-HT4 receptor levels before starting their treatment with the selective serotonin reuptake inhibitor escitalopram.
Patients who showed no improvement in depressive symptoms after 4 weeks (n = 14), as assessed by the Hamilton Depression Rating Scale 6 (HAMD6), were switched to the serotonin-norepinephrine reuptake inhibitor duloxetine.
Both escitalopram and duloxetine inhibit the reuptake of 5-HT4, enhancing neurotransmitter activity; escitalopram primarily increases serotonin levels, while duloxetine increases both serotonin and norepinephrine levels.
The primary cognitive outcome measure was change in the Verbal Affective Memory Task 26. Secondary cognitive outcomes were change in working memory, reaction time, emotion recognition bias, and negative social emotion.
After 8 weeks of treatment, a subset of 40 patients repeated PET scans, and at 12 weeks, all patients repeated cognitive testing.
Matching neuroimaging and cognitive data were available for 88 patients at baseline and for 39 patients with rescan.
As expected, the study showed that antidepressant treatment resulted in the downregulation of 5-HT4 receptor levels. “One hypothesis is that if we increase the availability of serotonin [with treatment], downregulation of the receptors might be a response,” said Dam.
“What was interesting was that this was the effect across all patients, whether they [clinically] responded or not. So we see the medication does what it’s supposed to do in the brain.” But, she said, there was no association between 5-HT4 receptor levels and HAMD6 scores.
Gains in Verbal Memory
Although the downregulation of 5-HT4 did not correlate with somatic or mood symptoms, it did correlate with cognitive symptoms.
Interestingly, while most patients showed improvement in depressive symptoms — many reaching remission or recovery — they also experienced gains in verbal memory. However, these improvements were not correlated. It was possible for one to improve more than the other, with no apparent link between the two, said Dam.
“What was linked was how the brain responded to the medication for this particular receptor. So even though there is this downregulation of the receptor, there’s still a lot of activation of it, and our thinking is that it’s activation of the receptor that is the important bit.”
Work by other groups has shown that another medication, prucalopride, which is used to treat gastroparesis, can more directly activate the 5-HT4 receptor, and that the treatment of healthy volunteers with this medication can boost memory and learning, said Dam.
“We could repurpose this drug, and we’re currently looking for funding to test this in a wide variety of different groups such as concussion, diabetes, and depression.”
The study’s co-investigator Vibe G. Frokjaer, MD, said more research is required to understand the potential implications of the findings.
“Poor cognitive function is very hard to treat efficiently and may require extra treatment. This work points to the possibility of stimulating this specific receptor so that we can treat cognitive problems, even aside from whether or not the patient has overcome the core symptoms of depression,” she said in a release.
Commenting on the research, Philip Cowen, MD, professor of psychopharmacology at the University of Oxford, Oxford, England, said in a release that in light of “recent controversies about the role of brain serotonin in clinical depression, it is noteworthy that the PET studies of the Copenhagen Group provide unequivocal evidence that brain 5-HT4 receptors are decreased in unmedicated depressed patients.” 
“Their work also demonstrates the intimate role of brain 5-HT4 receptors in cognitive function,” he added. “This confirms recent work from Oxford, showing that the 5-HT4 receptor stimulant, prucalopride — a drug licensed for the treatment of constipation — improves memory in both healthy participants and people at risk of depression,” he added.
The study was funded by the Innovation Fund Denmark, Research Fund of the Mental Health Services – Capital Region of Denmark, Independent Research Fund Denmark, Global Justice Foundation, Research Council of Rigshospitalet, Augustinus Foundation, Savværksejer Jeppe Juhl og hustru Ovita Juhls Mindelegat, Lundbeck Foundation, and H. Lundbeck A/S.
Dam reported serving as a speaker for H. Lundbeck. Frokjaer reported serving as a consultant for Sage Therapeutics and lecturer for H. Lundbeck, Janssen-Cilag, and Gedeon Richter. Study investigator Martin B. Jørgensen reports he has given talks on behalf of Boehringer Ingelheim and Lundbeck Pharma. All other investigators reported no relevant disclosures.
 
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